Avalanche Awareness

Avalanche History in Rogers Pass

Over 250 men died in avalanches in Rogers Pass between 1885 and 1911. The worst incident occurred during the night of March 4, 1910. A crew of 58 men were shovelling a previous avalanche from Cheops Mountain off the track. While they were working another ripped off the aptly named Avalanche Mountain on the opposite side of the valley. All but one man perished.

While our understanding of avalanches remains incomplete, we have come a long way since the early days of the Canadian Pacific Railway in Rogers Pass. This was Canada's first contact with avalanches on a large scale. While there was no attempt to predict periods of high avalanche hazard to avoid exposing workers to this threat, miles of snow sheds were constructed to protect the railway. The completion of the Connaught Tunnel in 1916 removed the railway from the most dangerous portion of the pass.

Derived from the French verb "avaler" (to swallow), a snow avalanche is among the most wondrous sights in nature, so long as it can be appreciated from a safe distance. Snow avalanches are the single greatest threat to winter recreation in the mountains.

The Science of Avalanche Hazard Evaluation

While no one can absolutely determine the stability of snow on a mountainside, there are some strong clues as to what is happening in a snowpack. The multitude of indicators for assessing snow stability range from the subtle (the shape of snow crystals) to the obvious (a meter of freshly fallen snow). Other factors include temperature, humidity, wind speed and direction, and underlying terrain. All must be considered relative to the intended route of travel. Knowing what is safe is just as important as recognizing a dangerous situation.

Avalanche hazard evaluation is most often accomplished by digging a snow profile. A smooth sided snow hole on a representative slope is dug carefully as to not disturb possible weak layers. Here the primary concern is to determine the relative strength of the layers of snow, which represent a recent history of past snowfalls. Each layer maintains some of the characteristics of that storm and bonds more or less well to the previous layer. How easily these layers can be separated is referred to as shear strength. Snow profiles must be done frequently in order to develop a sense of comparison. The strength of snow is relative.

Following the development of a snow pack over a winter helps us to stay in tune with conditions. A pattern will emerge depending on climate. The Coast Range and the Columbia Mountains have relatively mild temperatures and heavy snowfalls. Stability problems are usually in the upper part of the snowpack, a result of heavy recent precipitation or a buried weakness waiting to be overloaded.

The most notorious of these is a surface hoar layer. These feathery crystals form on the surface of the snow during a period of cold weather. Subsequent snowfalls bond poorly but manage to persist, sometimes building up to the thickness of a meter before rippingout as a slab avalanche.

A Rocky Mountain snowpack is usually much shallower and subject to much colder temperatures. This causes sublimation at the base of the snowpack creating depth hoar crystals, a process where larger crystals grow at the expense of smaller ones, changing snow to a sugar-like consistency. This weakness grows slowly over months, making it difficult to predict when it has deteriorated enough to release a slide. Intervening snowfalls and temperature changes complicate matters, making avalanche prediction as much an art as a science.

Where to Go to Learn More

While not everyone needs to become a snow scientist, all backcountry users should be attuned to avalanche information. Professional evaluations of conditions are available. Glacier National Park issues a daily avalanche bulletin for backcountry users as part of the avalanche control work conducted to protect Trans-Canada Highway traffic through Rogers Pass. Call 250-837-MTNS for a report that also includes backcountry travel conditions.

The Canadian Avalanche Association offers a similar service by pooling information from avalanche operations covering the southern portions of British Columbia and Alberta. Reach them at 1-800-667-1105 or www.avalanche.ca.

Travel Tips

Ski in a group that includes knowledgeable participants. Discuss and practice rescue techniques with your partners. Take part in route finding decisions. Ski touring is more of a team sport than it first appears.

Practice using a transceiver until you can find two of them in two minutes. Have someone bury it for you repeatedly. Use a plastic bag to keep moisture out of the unit. Don't forget to turn it on first.

Take an avalanche course. It's a fascinating subject and you'll meet interesting people.